Hi - Can anyone tell me whether Switched Multimegabit Data Service is a Cell Switched or Packet Switched WAN link please? In my Cisco notes it says it is Cell Switched along with ATM,however in the glossary it states... A high-speed, packet-switched, datagram-based WAN networking technology offered by the telephone companies.
Which is correct? Thanks
Hi,
I think it's more cell than packet. If I remember correctly there are two buses running in opposite directions forming a pseudo-ring ( Token-ring like ); in each bus there is a continuous stream of empty cells inserted by the Telco; a station then can "book" service by monitoring this stream of cells ( either in clockwise or counter clock wide direction ) so that if no other station has requested cells then this station can use them all. However SMDS is somewhat complex, not very efficient and cell structure is incompatible with ATM so I think it's not used anylonger now.
Regards, Gabriele
"daytime" ha scritto nel messaggio news: snipped-for-privacy@m58g2000cwm.googlegroups.com...
Switched Multimegabit Data Service (SMDS) is a telecommunications service that provides connectionless, high- performance, packet-switched data transport.
It is neither a PROTOCOL nor a TECHNOLOGY.
Rather, it supports standard protocols and communications interfaces using current (and future) technology.
SMDS allows users to transparently extend their data communications capabilities over a wider geographical area.
Since it is a SERVICE offered by the telephone companies, SMDS permits this expansion using existing Customer Premises Equipment (CPE) and protocols, with minimal investment in dedicated leased lines as the number of line terminations increases.
SMDS has been defined by the IEEE 802.6 Metropolitan Area Network (MAN) standard, as implemented by Bellcore.
It can use a variety of technologies, including Broadband ISDN (B-ISDN) and Distributed Queue Dual Bus (DQDB).
Current North American implementations utilize DQDB with DS1 (1.5 Mbit/s) or DS3 (45 Mbit/s) lines.
Other implementations utilize E1 lines at speeds in excess of 1.9 Mbit/s or E3 lines.
Future SMDS networks will couple B-ISDN with SONET OC3 at 155 Mbit/s.
The development of this service has paralleled the emerging Asynchronous Transfer Mode (ATM) standards.
Like ATM, SMDS uses cell relay TRANSPORT.
Both services use 53 octet cells for transport and can accommodate packet lengths of 9188 octets (However, the maximum length for SMDS is
9188 octets and the maximum length for ATM is 65535 octets.)Because of this, SMDS is considered to be an intermediate between the packet-switched services offered today and the ATM service of the future.
Sincerely,
Brad Reese
Both - although since it is more or less dead it probably doesnt matter....
The "hand off" from a router to the CPE is normally HSSI for high speed, and packets flow across the interface. Most services stopped at 34 to 50 Mbps
Within the WAN transmission - the UK service which was run by BT was cell based, even for links as slow as 2 Mbps.
And just to confuse the issue, BT also provided interworking with both ATM and Frame Relay WANs inside their network......
messagenews: snipped-for-privacy@m58g2000cwm.googlegroups.com...
doesnt matter....
Thanks for that
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