WAN overview

The software of the router provides the ability for holding a large range of network  , which can meet the demand of various network circumstances.

This chapter introduce some common guidances to configure following :

FR

LAPB and X.25

HDLC

SLIP

PPP

This chapter only give brief descriptions of these technologies, if you want to know more details, please refer to corresponding chapters.

 

FR

Frame relay of the router’s software support IP route and private line now.

   The software provides such functions: 

When all flux received by a DLCI can be transmit to the same next hop address by another DLCI,  you can use frame relay switching. In such a case, the software of the router does not need to check every frame to assure target address, so,it will reduce processing burden of the router.

LAPB and X.25

   X.25 is one of a group of specifications defined by ITU-T, these specifications are international standards, and they are called recommendations before.

ITU-T X.25 has defined how DTE and DCE are mainted for remote terminal access and computer computer communication.

The X.25 specification has defined two-layer protocols of the Open Systems Interconnection (OSI) reference model. The data link layer protocol is defined as Link Access Procedure, Balanced (LAPB). The network layer protocol is sometimes called the packet level protocol(PLP), but it is always called the X.25 protocol(although less correctly) .  

The ITU-T updates its Recommendations periodically. The specifications published in 1980 and 1984 are most common versions. In addition,the international standards organization (ISO) has published ISO 7776:1986 which is equal to the LAPB standard, and ISO 8208:1989 which is equal to the ITU-T 1984 X.25 recommendation packet layer.

The router’s x.25 follows the ITU-T 1982 x.25 recommendation,but its defence data network(DDN) and blacker front end (BFE) operation follow the ITU-T 1980 X.25 recommendation.

Note:the ITU-T executes the functions of the former consultative committee for international telegraph and teleohone(ccitt).The 1988 X.25 standard was the last CCITT recommendation. The first ITU-T recommendation was the 1993 version.    

Except providing remote terminal access, the router’s X.25 software provides transport for IP(LAN protocols).

In a brief, the X.25 software provides following functions:

  The router’s software X.25 realization does not support quick switching.

HDLC

High-level data link control protocol(HDLC)is derived from synchronization data link control protocol (SDLC) in SNA of IBM.After developing SDLC, IBM provides it to ANSI AND ISO, dividing them to America standard and international standard. And ANSI modified this protocol to advanced data communication CONTROL protocol(ADCCP);ISO modified this protocol to HDLC. Later,CCITT adopted and modified HDLC, and became a part of link access protocol (LAP) and X.25 interface standard. HDLC is a protocol facing to byte ,which guarantees clarities of data.

HDLC is a data packet protocol, it defines an linking encapsulation to IP packet on synchronization, and run TCP/IP on point-to-point serial line.   

HDLC is usually used to DDN lines, and it is a simple and high-efficiency protocol.

SLIP

Whatever it is a router-router linking way or it is a dialing-host to router linking way, point-point data linking layer protocol(such as SLIP,PPP) is need in line to encapsulate frame and control errors.  

SLIP is a data packeted protocol, it defines a series of strings to encapsulate IP packet on serial line, and it is used to run TCP/IP on point-point serial line.   

The realization of SLIP accord to RFC 1055, support TCP/IP header compression recommendated by RFC 1144 ,and SLIP supports that various network devices and hosts realize connection with each other through SLIP protocol.

PPP

PPP provides multiple-protocol transportation on point-point link. The router’s main fucntions are: 

①.It obeys RFC 1661 and supports link controlling protocol(LCP),is used to setup,configure and test data link.

②.It obeys RFC 1662 and supports IP encapsulation on PPP, and it can realize IPCP on NCP.

③.It obeys RFC 1334 and support several common authentication protocol ,including PAP,CHAP,MC-CHAP and TACACS+.

④.It obeys RFC 1144 and support TCP/IP header compression, and it can advance efficiency data throughput.

⑤.It provides broad chooses of items, can adapt many conditions, and it support to link to all kinds of network equipments and hosts through PPP.

⑥.It support synchronism and asynchronism PPP .

⑦.It support PPP multilink ,can realize multiple-link binding.

⑧.It can support “call back”, provides more safety.

⑨.It can support RADIUS ,can realize authentication to user ,authorization and accouting when the router is used as a dialing server. The information of users are saved in a host, which switch information with routers through RADIUS.