Minimum length required is 4 octets, except for Keepalive messages. The maximum TLV length is The range of administratively-scoped addresses can be subdivided by administrators so that multiple levels of administrative boundaries can be simultaneously supported.
Typically servers will cache the information learned from MZAP and can then provide this information to applications in a timely fashion upon request using other means, e. If 1, address allocators should not use the entire range, but should learn an appropriate subrange via another mechanism. The count may be zero. For example, if the zone is a boundary for PGM has no notion of group membership.
It simply provides reliable multicast data delivery within a transmit window advanced by a source according to a purely local strategy. PGM guarantees that a receiver in the group either receives all data packets from transmissions and repairs, or is able to detect unrecoverable data packet loss.
Rather, PGM is best suited to those applications in which members may join and leave at any time, and that are either insensitive to unrecoverable data packet loss or are prepared to resort to application recovery in the event. T -- Packet is a parity packet for a transmission group of variable sized packets.
P -- Packet is a parity packet. All PIM protocols share a common control message format. We focus on the Dense Mode in this document. ISPs typically appreciate the ability to use any underlying unicast routing protocol with PIM-DM because they need not introduce and manage a separate routing protocol just for RPF checks. We focus on the Sparse Mode in this document.
The protocol is not dependent on any particular unicast routing protocol, and is designed to support sparse groups. It uses the traditional IP multicast model of receiver-initiated membership, supports both shared and shortest-path trees, and uses soft-state mechanisms to adapt to changing network conditions.
Receivers signal to routers in order to join the multicast group that will receive the data. Source trees directly connect sources to receivers. There is a separate tree for every source. Source trees are considered shortest-path trees from the perspective of the unicast routing tables. PIM-SM can use either type of tree or both simultaneously.
We focus on version 2, which is widely deployed. LSPs are virtual tunnels that are formed by a sequence of labels at each and every node along the path from the source to the destination. With its powerful new features and abilities to interface with legacy technologies, MPLS has become a solution for the next generation backbone networks for multiple services such as data, voice and video over the same network. In this section, we focus on the MPLS framework. When a labeled packet is received, the label value at the top of the stack is looked up and the system learns: a the next hop to which the packet is to be forwarded; b the operation to be performed on the label stack before forwarding; this operation may be to replace the top label stack entry with another, or to pop an entry off the label stack, or to replace the top label stack entry and then to push one or more additional entries on the label stack.
The common control plane promises to simplify network operation and management by automating end-to-end provisioning of connections, managing network resources, and providing the level of QoS that is expected in the new applications. In a single session, each peer is able to learn about the others label mappings, in other words, the protocol is bi-directional.
It contains extensions for LDP to extend its capabilities such as setup paths beyond what is available for the routing protocol. The LSR uses this protocol to establish label switched paths through a network by mapping network layer routing information directly to data-link layer switched paths.
The present number is 1. The lst 2 indicate a label space within the LSR. There are both mandatory and optional parameters. Some messages have no mandatory parameters, and some have no optional parameters. It also supports smooth rerouting of LSPs, preemption, and loop detection. The ingress node of an LSP Label Switched Path uses a number of methods to determine which packets are assigned a particular label. In fact, the IPv4 v6 that appears in the object name only denotes that the destination address is an IPv4 v6 address.
A tunnel ID is part of the Session object. For example, in IP Version 4, an address is 32 bits long. In an Ethernet local area network, however, addresses for attached devices are 48 bits long. ARP provides the rules for making this correlation and providing address conversion in both directions. Details of RARP are presented in a separate document. IPCP packets received before this phase is reached should be silently discarded. Each end of the link must separately request this option if bidirectional compression is desired.
IPv6CP packets received before this phase is reached should be silently discarded. Assuming that an entry has been set up in the router table, the RARP server will return the IP address to the machine, which can store it for future use.
SLIP is commonly used on dedicated serial links and sometimes for dialup purposes, and is usually used with line speeds between bps and To send a packet, a SLIP host simply starts sending the data in the packet. If a data byte is the same code as the END character, a two byte sequence of ESC and octal decimal is sent instead.
When the last byte in the packet has been sent, an END character is then transmitted. This compression improves throughput for interactive sessions noticeably. To address these issues, various network and information security technologies have been developed by various organizations and technology vendors. Here is a summary of the technologies: AAA: Authorization, Authentication and Accounting is a technology for intelligently controlling access to network resources, enforcing policies, auditing usage, and providing the information necessary to bill for services.
Authentication provides a way of identifying a user, typically by having the user enter a valid user name and valid password before access is granted. The authorization process determines whether the user has the authority to access certain information or some network sub-domains.
A dedicated AAA server or a program that performs these functions often provides authentication, authorization, and accounting services. VPN: Virtual Private Network is a technology allowing private communications by business and individuals, such as remote access to a corporate network or using a public telecommunication infrastructure, such as the Internet. Various network-tunneling technologies such as L2TP have been developed to reach this goal. Using encryption technologies such as IPsec could further enhance information privacy over network and virtual private networks.
If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded. Kerberos performs authentication under these conditions as a trusted third-party authentication service by using conventional cryptography, i.
The session key now shared by the client and server is used to authenticate the client, and may optionally be used to authenticate the server. It may also be used to encrypt further communication between the two parties or to exchange a separate sub-session key to be used to encrypt further communication. The authentication exchanges mentioned above require readonly access to the Kerberos database.
The administration protocol is not described in this document. There is also a protocol for maintaining multiple copies of the Kerberos database, but this can be considered an implementation detail and may vary to support different database technologies.
The client is responsible for passing user information to designated RADIUS servers, and then acting on the response which is returned. Extensible Protocol: All transactions are comprised of variable length Attribute-Length-Value 3-tuples.
New attribute values can be added without disturbing existing implementations of the protocol. It may optionally also provide compression. SSH-Trans provides strong encryption, cryptographic host authentication, and integrity protection. Authentication in this protocol level is host-based; this protocol does not perform user authentication.
A higher level protocol for user authentication can be designed on top of this protocol. It runs over the user authentication protocol. The client sends a service request once a secure transport layer connection has been established. A second service request is sent after user authentication is complete.
The connection protocol provides channels that can be used for a wide range of purposes. For details of the message formats, please refer to the Reference documents listed below. Layer Two Forwarding protocol L2F permits the tunneling of the link layer i. Using such tunnels, it is possible to divorce the location of the initial dial-up server from the location at which the dial-up protocol connection is terminated and access to the network provided. This is part of the authentication process.
With L2TP, a user has an L2 connection to an access concentrator e. This allows the actual processing of PPP packets to be divorced from the termination of the L2 circuit. Because L2TP makes a PPP session appear at a location other than the physical point at which the session was physically received, it can be used to make all channels appear at a single NAS, allowing for a multilink operation even when the physical calls are spread across distinct physical NASs.
L2TP utilizes two types of messages, control messages and data messages. Control messages are used in the establishment, maintenance and clearing of tunnels and calls. Data messages are used to encapsulate PPP frames being carried through the tunnel. Data messages are not retransmitted when packet loss occurs. It is set to 0 for data messages and 1 for control messages. Must be set for control messages.
All reserved bits are set to 0 on outgoing messages and are ignored on incoming messages. S must be set for control messages. This bit is set to 0 for control messages. This indicates a version 1 L2TP message. No other systems need to be aware of PPTP.
Its basic purpose is to allow the receiver to ensure that it is properly synchronized with the TCP data stream. Service differentiation is desired to accommodate heterogeneous application requirements and user expectations, and to permit differentiated pricing of Internet service. Within the core of the network, packets are forwarded according to the per-hop behavior associated with the DS codepoint.
In the most general case, a system has a packet, namely a payload, which needs to be encapsulated and delivered to some destination. The resulting GRE packet can then be encapsulated in some other protocol and then forwarded. This outer protocol is called the delivery protocol. Care should be taken when forwarding such a packet, since if the destination address of the payload packet is the encapsulator of the packet i.
In this case, the packet MUST be discarded. Because these services are provided at the IP layer, they can be used by any higher layer protocol, e. These mechanisms also are designed to be algorithm-independent.
This modularity permits selection of different sets of algorithms without affecting the other parts of the implementation. For example, different user communities may select different sets of algorithms creating cliques if required.
Protocol Structure IPsec Architecture includes many protocols and algorithms. This protection service against replay is an optional service to be selected by the receiver when a Security Association is established. AH provides authentication for as much of the IP header as possible, as well as for upper level protocol data.
Thus the protection provided to the IP header by AH is only partial in some cases. Security services can be provided between a pair of communicating hosts, between a pair of communicating security gateways, or between a security gateway and a host.
The primary difference between the authentications provided by ESP and by AH is the extent of the coverage. For more details on how to use AH and ESP in various network environments, see the reference documents. The ESP header is inserted after the IP header and before the upper layer protocol header transport mode or before an encapsulated IP header tunnel mode. ESP consists of an unencrypted header followed by encrypted data. The set of services provided depends on options selected at the time of Security Association establishment and on the placement of the implementation.
The anti-replay service may be selected only if data origin authentication is selected, and its election is solely at the discretion of the receiver.
IKE processes can be used for negotiating virtual private networks VPNs and also for providing a remote user from a remote site whose IP address need not be known beforehand access to a secure host or network.
Client negotiation is supported. Client mode is where the negotiating parties are not the endpoints for which security association negotiation is taking place. When used in client mode, the identities of the end parties remain hidden. For more details, see the reference documents.
These formats provide a consistent framework for transferring key and authentication data independent of the key generation technique, encryption algorithm and authentication mechanism.
ISAKMP is distinct from key exchange protocols in order to clearly separate the details of security association management and key management from the details of key exchange. There may be many different key exchange protocols, each with different security properties.
However, a common framework is required for agreeing to the format of SA attributes, and for negotiating, modifying, and deleting SAs. Separating the functionality into three parts adds complexity to the security analysis of a complete ISAKMP implementation. However, the separation is critical for interoperability between systems with differing security requirements, and should also simplify the analysis of further evolution of an ISAKMP server.
By centralizing the management of the security associations, ISAKMP reduces the amount of duplicated functionality within each security protocol. The keys for this symmetric encryption are generated uniquely for each connection and are based on a secret negotiated by another protocol such as the TLS Handshake Protocol. The Record Protocol can also be used without encryption. The Record Protocol can operate without a MAC, but is generally only used in this mode while another protocol is using the Record Protocol as a transport for negotiating security parameters.
This authentication can be made optional, but is generally required for at least one of the peers. One advantage of TLS is that it is application protocol independent. Because SSL is a transportlayer service, an SSL VPN has the advantage of being able to apply this access control at transport- and application-layers, providing greater granularity of control.
We only summarize the protocols here without details, which can be found in the reference documents. TLS Record Protocol is a layered protocol. The Record Protocol takes messages to be transmitted, fragments the data into manageable blocks, optionally compresses the data, applies a MAC, encrypts, and transmits the result.
TLS Record Layer receives uninterrupted data from higher layers in non-empty blocks of arbitrary size. Key calculation: The Record Protocol requires an algorithm to generate keys, IVs, and MAC secrets from the security parameters provided by the handshake protocol. TLS Handshake Protocol: consists of a suite of three sub-protocols which are used to allow peers to agree upon security parameters for the record layer, authenticate themselves, instantiate negotiated security parameters, and report error conditions to each other.
It also adapts the addressing scheme to encompass domainname and IPv6 addresses. VOIP signaling protocols are used to set up and tear down calls, carry information required to locate users and negotiate capabilities.
There are a few VOIP protocol stacks which are derived by various standard bodies and vendors, namely H. The standard encompasses both point to point communications and multipoint conferences. Terminals, gateways and MCUs are known as endpoints. SIP is an application layer control protocol for creating, modifying and terminating sessions with one or more participants. Requests are generated by the client and sent to the server.
The server processes the requests and then sends a response to the client. A request and the responses for that request make a transaction. In the MGCP architecture, the call control intelligence is located outside the gateways and is handled by the call control elements the Call Agent.
Also, the call control elements Call Agents will synchronize with each other to send coherent commands to the gateways under their control. For voice communications over IP to become acceptable to users, the packet delay and getter needs to be less than a threshold value.
Gateway technologies are being developed to bridge the two networks. Many network management and user management technologies and products are being developed to address the issue. In addition to voice applications, H. The components under H. Terminal represents the end device of every connection. It provides real time two way communications with another H. This communication consists of speech, speech and data, speech, and video, or a combination of speech, data and video.
Gateways establish the connection between the terminals in the H. Gatekeepers are responsible for translating between telephone number and IP addresses. They also manage the bandwidth and provide a mechanism for terminal registration and authentication. Gatekeepers also provide services such as call transfer, call forwarding etc. MCUs take care of establishing multipoint conferences. Protocol Structure The protocols in the H. The top layers T. Details of each protocols will be discussed in separate documents.
This is achieved by exchanging H. The callsignaling channel is opened between two H. The ITU H. This port initiates the Q. When a gateway is present in the network zone, H. The gatekeeper decides the method chosen during the RAS admission message exchange. If no gatekeeper is present, H. The RAS is used to perform registration, admission control, bandwidth changes, status, and disengage procedures between endpoints and gatekeepers.
This signaling channel is opened between an endpoint and a gatekeeper prior to the establishment of any other channel. May be up to 2 octets in length. May be sent unsolicited by terminal to gatekeeper at predetermined intervals. In particular, H. The scope of H. This parallels the concept that the support of H. Figure H. The H. The messages carried include messages to exchange capabilities of terminals and to open and close logical channels. After a connection has been set up via the call signaling procedure, the H.
It also manages the call after it has been established. Used for opening and closing logical channels, which are multiplexed paths between the endpoints used for data transfer.
Using this command, at any point during the conference, the receiving endpoint can request a change in mode of the transmitted information provided the mode is in the transmit capability of the transmitter. Used by the multipoint controller for selecting a common mode of operation in a multipoint conference.
Used for controlling a multipoint conference, e. Used for measuring the roundtrip delay between two endpoints on the control channel. Used for requesting updates for video frames, in case of data loss. After this command the endpoints close all logical channels, drop the call and inform the gatekeeper about the end of the call.
Protocol Structure H. Key H. Possible replies: Acknowledge, Reject, Release in case of a time out. Possible replies: Acknowledge, Reject, Release. Open Logical Channel Opens a logical channel for transport of audiovisual and data information. Close Logical Channel Closes a logical channel between two endpoints. Possible replies: Acknowledge Request Mode Used by a receive terminal to request particular modes of transmission from a transmit terminal.
Send Terminal Capability Set Commands the far-end terminal to indicate its transmit-and-receive capabilities by sending one or more Terminal Capability Sets.
End Session Command Indicates the end of the H. After transmission, the terminal will not send any more H. A termination may have more than one stream, and therefore a context may be a multistream context. Audio, video, and data streams may exist in a context among several terminations.
The following is a list of the commands: 1. The Subtract command on the last Termination in a Context deletes the Context. Move -- The Move command automatically moves a Termination to another context.
AuditValue -- The AuditValue command returns the current state of properties, events, signals and statistics of Terminations. AuditCapabilities -- The AuditCapabilities command returns all the possible values for Termination properties, events and signals allowed by the Media Gateway. ServiceChange -- The ServiceChange Command allows the Media Gateway to notify the Media Gateway Controller that a Termination or group of Terminations is about to be taken out of service or has just been returned to service.
Media gateways contain endpoints on which the Call Agent can create, modify and delete connections in order to establish and control media sessions with other multimedia endpoints.
A media gateway is typically a network element that provides conversion between the audio signals carried on telephone circuits and data packets carried over the Internet or over other packet networks. The Call Agent can instruct the endpoints to detect certain events and generate signals. The endpoints automatically communicate changes in service state to the Call Agent. Furthermore, the Call Agent can audit endpoints as well as the connections on endpoints.
It assumes that Call Agents will synchronize with each other to send coherent commands and responses to the gateways under their control. MGCP assumes a connection model where the basic constructs are endpoints and connections. Creation of physical endpoints requires hardware installation, while creation of virtual endpoints can be done by software.
Connections may be either point to point or multipoint. A point to point connection is an association between two endpoints with the purpose of transmitting data between these endpoints.
Once this association is established for both endpoints, data transfer between these endpoints can take place. A multipoint connection is established by connecting the endpoint to a multipoint session. Connections can be established over several types of bearer networks. In the MGCP model, the gateways focus on the audio signal translation function, while the Call Agent handles the call signaling and call processing functions. The transactions are composed of a command and a mandatory response.
The Point-to-Point Protocol PPP provides a standard method for transporting multi-protocol datagrams over point-to-point links. These connections offer a packet delivery service that includes error detection, but does not do error correction.
With this model, each host utilizes its own PPP stack and the user is presented with a familiar user interface. Access control, billing and type of service can be done on a per-user, rather than per-site, basis. PPPoE includes a discovery protocol that provides this. PPPoE has two distinct stages. In the Discovery process, a Host the client discovers an Access Concentrator the server.
Based on the network topology, there may be more than one Access Concentrator that the Host can communicate with. The Discovery stage allows the Host to discover all Access Concentrators and then select one. When Discovery completes successfully, both the Host and the selected Access Concentrator have the information they will use to build their point-to-point connection over Ethernet.
The Discovery stage remains stateless until a PPP session is established. Related Protocols PPP, Frame Relay is based on packet-switched technologies similar to x. It employs the following two packet techniques: a Variable-length packets and b Statistical multiplexing. It does not guarantee data integrity and discard packets when there is network congestion.
In reality, it still delivers data with high reliability. The Frame Relay frame is transmitted to its destination through virtual circuits, which are logical paths from an originating point in the network to a destination point. A number of virtual circuits can be multiplexed into a single physical circuit for transmission across the network.
This capability often can reduce the equipment and network complexity required to connect multiple terminal devices.
A virtual circuit can pass through any number of intermediate switches located within the Frame Relay packet switched network. PVCs are set up administratively by the network manager for a dedicated point-to-point connection; SVCs are set up on a call-by-call basis using the same signaling as for ISDN set up. Status messages include keepalives and PVC status messages. The later is the more popular implementation. HDLC is part of the X. LAPB is a bit-oriented synchronous protocol that provides complete data transparency in a full-duplex point-to-point operation.
It supports a peer-to-peer link in which neither end of the link plays the role of the permanent master station. This kind of situation occurs, for instance in satellite communication. When set to false it indicates an additional byte follows. In addition, it includes sequence numbers, control features and error tracking according to the frame type. LAPB makes sure that frames are error free and properly sequenced.
The station initiating the call is determined to be the primary, and the responding station the secondary. In the response frame this same bit becomes the receivers Final bit.
The receiver always turns on the Final bit in its response to a command from the sender with the Poll bit set. Iframes carry send-and-receive sequence numbers. S-frame functions include requesting and suspending transmissions, reporting on status, and acknowledging the receipt of I-frames.
S-frames carry only receive sequence numbers. U-frame functions include link setup and disconnection, as well as error reporting. U-frames carry no sequence numbers. This mode is totally balanced i. Each station may initialize, supervise, recover from errors, and send frames at any time. Subscribers are charged based on their use of the network. The DTE device that receives the request can either accept or refuse the connection.
If the request is accepted, the two systems begin fullduplex information transfer. Either DTE device can terminate the connection. After the session is terminated, any further communication requires the establishment of a new session. Both switched and permanent virtual circuits are used. The X. The Physical Level: describes the interface with the physical environment. There are three protocols in this group: 1 X. The Packet Layer Protocol PLP : describes the data transfer protocol in the packet switched network at the network layer layer 3.
We focus on the X. Protocol Structure X. The control packet as well as all X. The additional information for each message is different. The fourth byte of the packet tells why the connection is being cleared. These devices may be connected through wired cables or wireless links. Ethernet is by far the most commonly used LAN technology. Token Ring technology is still used by some companies. LANs are traditionally used to connect a group of people who are in the same local area.
Local Area Network protocols are mostly at the data link layer layer 2. In the Ethernet standard, there are two modes of operation: half-duplex and full-duplex. Therefore, the carrier extension technique is used to ensure the minimum frame size of bytes in Gigabit Ethernet to achieve a reasonable link distance. Each Ethernet-equipped computer operates independently of all other stations on the network: there is no central controller.
All stations attached to an Ethernet are connected to a shared signaling system, also called the medium. The Ethernet system consists of three basic elements: 1 the physical medium used to carry Ethernet signals between computers, 2 a set of medium access control rules embedded in each Ethernet interface that allows multiple computers to fairly arbitrate access to the shared Ethernet channel, and 3 an Ethernet frame that consists of a standardized set of bits used to carry data over the system.
The IEEE After each frame transmission, all stations on the network must contend equally for the next frame transmission opportunity. Access to the shared channel is determined by the medium access control MAC mechanism embedded in the Ethernet interface located in each station.
As each Ethernet frame is sent onto the shared signal channel, all Ethernet interfaces look at the destination address. If the destination address of the frame matches with the interface address, the frame will be read entirely and be delivered to the networking software running on that computer. All other network interfaces will stop reading the frame when they discover that the destination address does not match their own address. The signal topology of the Ethernet is also known as the logical topology, to distinguish it from the actual physical layout of the media cables.
The logical topology of an Ethernet provides a single channel or bus that carries Ethernet signals to all stations. Multiple Ethernet segments can be linked together to form a larger Ethernet LAN using a signal amplifying and retiming device called a repeater. Most importantly, segments must never be connected in a loop. Every segment in the system must have two ends, since the Ethernet system will not operate correctly in the presence of loop paths. Even though the media segments may be physically con- LAN - Ethernet Protocols Protocols Guide nected in a star pattern, with multiple segments attached to a repeater, the logical topology is still that of a single Ethernet channel that carries signals to all stations.
The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the framereception portions of receiving physical layers with the incoming bit stream. The SOF is an alternating pattern of ones and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-most bit in the leftmost byte of the destination address.
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